Added horizontal scroll to go to next/previous weeks.
* Horizontal scroll only moves 1 day at a time.
* When clicking on the < and > buttons, still goes back/forward @numdays.
Goes to the beginning of the next/previous week when pressing < and > buttons.
Added a label to show current year.
Added color as a Task variable.
* Added random_color function to generate similar colors.
Fixed bug when drawing tasks overflowing to both sides.